title: Computational analysis shows why transcranial alternating current stimulation induces retinal phosphenes.
abstract: OBJECTIVE
  Transcranial alternating current stimulation (tACS), which is a novel technique for the manipulation of cortical oscillations, can generate subjective visual sensations (phosphenes). In this work, we computationally investigate the current that reaches the eyes from tACS electrodes in order to show that phosphenes induced by tACS are retinal in origin.
  
  
  METHODS
  The finite-element method is used for modelling the path of the current in an anatomically realistic model of the head for various electrode montages. The computational results are used for analysing previous experimental data to investigate the sensitivity of the eye to electrical stimulation.
  
  
  RESULTS
  Depending on the locations of both the stimulating and reference electrodes, a small portion of the stimulation current chooses a path that goes through the eyes. Due to the sensitivity of the retina to electrical stimulation, even distant electrodes can produce a sufficiently strong current at the eyes for inducing retinal phosphenes.
  
  
  CONCLUSIONS
  The interference from retinal phosphenes needs to be considered in the design of tACS experiments. The occurrence of phosphenes can be reduced by optimizing the locations of the electrodes, or potentially increasing the number of reference electrodes to two or more. Computational modelling is an effective tool for guiding the electrode positioning.
authors.affiliation: Department of Computer Science and Engineering, Nagoya Institute of Technology, Nagoya, Japan. laakso.ilkka@nitech.ac.jp
authors.forename: Ilkka
authors.initials: I
authors.lastname: Laakso
authors.forename: Akimasa
authors.initials: A
authors.lastname: Hirata
mesh_terms: D000818:Animals; D003198:Computer Simulation; D006801:Humans; D008959:Models, Neurological; D010719:Phosphenes / Q000502:physiology*; D012160:Retina / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D014793:Visual Cortex / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*